For fiction: it's a hard tossup between Snow Crash and The Moon is a Harsh Mistress, though Ender's Game, The Bicentennial Man, Rendezvous with Rama series, and Atlas Shrugged also would be contenders for me.

For nonfiction: some current contenders would be Democracy: The God that Failed, The Physics of Immortality (very thought-provoking and mind-bending), and some of Robert Green's books particularly The 48 Laws of Power.